LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lighting. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desired illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption. Therefore, when taking into account all factors, they would typically be considered as a cost effective lighting option.
Typical LED tube lamps have a lamp tube, a circuit board disposed inside the lamp tube with light sources being mounted on the circuit board, and end caps accompanying a power supply provided at two ends of the lamp tube with the electricity from the power supply transmitting to the light sources through the circuit board. However, existing LED tube lamps have certain drawbacks. For example, the typical circuit board is rigid and allows the entire lamp tube to maintain a straight tube configuration when the lamp tube is partially ruptured or broken, and this gives the user a false impression that the LED tube lamp remains usable and is likely to cause the user to be electrically shocked upon handling or installation of the LED tube lamp.
Conventional circuit design of LED tube lamps typically doesn't provide suitable solutions for complying with relevant certification standards. For example, since there are usually no electronic components in a fluorescent lamp, it's fairly easy for a fluorescent lamp to be certified under EMI (electromagnetic interference) standards and safety standards for lighting equipment as provided by Underwriters Laboratories (UL). However, there are a considerable number of electronic components in an LED tube lamp, and therefore consideration of the impacts caused by the layout (structure) of the electronic components is important, resulting in difficulties in complying with such standards.
Further, the driving of an LED uses a DC driving signal, but the driving signal for a fluorescent lamp is a low-frequency, low-voltage AC signal as provided by an AC powerline, a high-frequency, high-voltage AC signal provided by a ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp may not achieve the LED tube lamp's compatibility with traditional driving systems of a fluorescent lamp.
Currently, LED tube lamps used to replace traditional fluorescent lighting devices can be primarily categorized into two types. One is for ballast-compatible LED tube lamps, e.g., T-LED lamp, which directly replaces fluorescent tube lamps without changing any circuit on the lighting device; and the other one is for ballast by-pass LED tube lamps, which omit traditional ballast on their circuit and directly connect the commercial electricity to the LED tube lamp. The latter LED tube lamp is suitable for the new surroundings in fixtures with new driving circuits and LED tube lamps. The ballast-compatible LED tube lamp is also known as “Type-A” LED tube lamp, and the ballast by-pass LED tube lamp provided with a lamp driving circuit is also known as a “Type-B” LED tube lamp. In the prior art, when a Type-B LED tube lamp has an architecture with dual-end power supply and one end cap thereof is inserted into a lamp socket but the other is not, since the lamp socket corresponding to the Type-B LED tube lamp is configured to directly receive the commercial electricity without passing through a ballast, an electric shock situation could take place for the user touching the metal or conductive part of the end cap which has not been inserted into the lamp socket. In addition, due to the frequency of the voltage provided from the ballast being much higher than the voltage directly provided from the commercial electricity/AC mains, the skin effect occurs when the leakage current is generated in the Type-A LED tube lamp, and thus the human body would not be harmed by the leakage current.
Therefore, since the Type-B LED tube lamp has higher risk of electric shock/hazard, compared to the Type-A, the Type B-LED tube lamp is requested to have extremely low leakage current for meeting the strict requirements in the safety certification standard (e.g., UL, CE, GS).
Due to the above technical issues, even many well-known international luminaries and LED lamps manufacturers also strand at the bottleneck on development of the ballast by-pass/Type-B LED tuba lamps having dual-end power supply structure. Taking GE lighting corporation for the example, according to the marketing material titled “Considering LED tubes” published on Jul. 8, 2014, and the marketing material titled “Dollars&Sense: Type-B LED Tubes” published on Oct. 21, 2016, GE lighting corporation asserts, over and over again, that the drawback of the risk of electric shock that occurs in the Type-B LED tube lamp cannot be overcome, and thus GE lighting corporation would not perform further product commercialization and sales consideration.
In the prior art, a solution of disposing a mechanical structure on the end cap for preventing electric shock is proposed. In this electric shock protection design, the connection between the external power and the internal circuit of the tube lamp can be cut off or established by the mechanical component's interaction/shifting when a user installs the tube lamp, so as to achieve the electric shock protection.